Wireless power transfer pad with multiple windings and magnetic pathway between windings

ABSTRACT

A wireless power transfer (“WPT”) pad apparatus includes a ferrite structure and four windings adjacent to the ferrite structure. A horizontal surface of the ferrite structure is adjacent to each of the four windings and each of the four windings are wound in a horizontal pattern that is planar to the horizontal surface. The four windings are arranged in a two-by-two square pattern in a north-south-north-south polarity arrangement.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/609,947 entitled “WIRELESS POWER TRANSFER PAD WITHMULTIPLE WINDINGS AND MAGNETIC PATHWAY BETWEEN WINDINGS” and filed onDec. 22, 2017 for Patrice Lethellier et al., which is incorporatedherein by reference.

FIELD

This invention relates to wireless power transfer and more particularlyrelates to a wireless power transfer pad with multiple windings and amagnetic pathway between windings.

BACKGROUND

As wireless power transfer (“WPT”) technology increases, there is a needto increase the amount of power transferred wirelessly. Practical sizeand power limits of components and switching devices limit the amount ofpower that can be transferred without paralleling devices, such asresonant converters. However, paralleling can cause unequal sharingbetween devices, which can cause unequal wear and component failure.

SUMMARY

A wireless power transfer (“WPT”) pad apparatus includes a ferritestructure and four windings adjacent to the ferrite structure. Ahorizontal surface of the ferrite structure is adjacent to each of thefour windings and each of the four windings are wound in a horizontalpattern that is planar to the horizontal surface. The four windings arearranged in a two-by-two square pattern in a north-south-north-southpolarity arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem with a low voltage wireless power transfer (“WPT”) pad;

FIG. 2A is a schematic block diagram illustrating one embodiment of apower converter apparatus;

FIG. 2B is a schematic block diagram illustrating one embodiment of apower converter apparatus with multiple resonant converters feedingwindings of one or more WPT pads and/or windings;

FIG. 3A is a schematic block diagram illustrating one embodiment of asecondary circuit feeding a load;

FIG. 3B is a schematic block diagram illustrating one embodiment ofseveral windings of a secondary pad feeding several secondary circuits,which feed a load;

FIG. 4 is a schematic block diagram illustrating one embodiment of a lowvoltage WPT pad;

FIG. 5 is a schematic block diagram illustrating one embodiment of a lowvoltage WPT pad with two parallel windings;

FIG. 6 is a schematic block diagram illustrating one embodiment of a WPTpad with four windings with a ferrite structure removed;

FIG. 7 is a schematic block diagram illustrating one embodiment of a WPTpad with four windings with a ferrite structure included;

FIG. 8 is a schematic block diagram illustrating one embodiment of across section of a primary pad and a secondary pad, each with a ferritechimney and a vertical shield;

FIG. 9 is a schematic block diagram illustrating one embodiment of asimplified ferrite structure of a four winding WPT pad and verticalshields depicting shunting of a stray electromagnetic field;

FIG. 10 is a schematic block diagram illustrating one embodiment of acenter section of a winding with capacitors; and

FIG. 11 is a schematic block diagram illustrating one embodiment of awinding structure that guides conductors within a winding;

FIG. 12 is a schematic block diagram illustrating one embodiment of afractional winding;

FIG. 13A is a schematic block diagram illustrating one embodiment of awinding with four conductors in parallel connected to compensate for avariation in winding length where the windings include a capacitorbetween windings;

FIG. 13B is a simplified schematic block diagram illustrating thewinding of FIG. 13A;

FIG. 13C is a schematic block diagram illustrating one embodiment of awinding with four conductors in parallel connected to compensate for avariation in winding length;

FIG. 13D is a simplified schematic block diagram illustrating thewinding of FIG. 13C; and

FIG. 14 is a schematic block diagram illustrating one embodiment of awinding with two windings in parallel connected to compensate for avariation in winding length where winding starting and ending points areadjusted to compensate for length variations.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment, but mean “one or more but not all embodiments” unlessexpressly specified otherwise. The terms “including,” “comprising,”“having,” and variations thereof mean “including but not limited to”unless expressly specified otherwise. An enumerated listing of itemsdoes not imply that any or all of the items are mutually exclusiveand/or mutually inclusive, unless expressly specified otherwise. Theterms “a,” “an,” and “the” also refer to “one or more” unless expresslyspecified otherwise.

Furthermore, the described features, structures, or characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details areprovided, such as examples of programming, software modules, userselections, network transactions, database queries, database structures,hardware modules, hardware circuits, hardware chips, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention may bepracticed without one or more of the specific details, or with othermethods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

The schematic flow chart diagrams included herein are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of one embodiment of the presented method.Other steps and methods may be conceived that are equivalent infunction, logic, or effect to one or more steps, or portions thereof, ofthe illustrated method. Additionally, the format and symbols employedare provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed in the flow chart diagrams, theyare understood not to limit the scope of the corresponding method.Indeed, some arrows or other connectors may be used to indicate only thelogical flow of the method. For instance, an arrow may indicate awaiting or monitoring period of unspecified duration between enumeratedsteps of the depicted method. Additionally, the order in which aparticular method occurs may or may not strictly adhere to the order ofthe corresponding steps shown.

A wireless power transfer (“WPT”) pad apparatus includes a ferritestructure and four windings adjacent to the ferrite structure. Ahorizontal surface of the ferrite structure is adjacent to each of thefour windings and each of the four windings are wound in a horizontalpattern that is planar to the horizontal surface. The four windings arearranged in a two-by-two square pattern in a north-south-north-southpolarity arrangement.

In some embodiments, for adjacent windings of the four windings theferrite structure comprises a magnetic pathway. In other embodiments, aferrite pathway between adjacent windings of the four windings has athickness and a width to provide a low impedance, unsaturated magneticpathway for an electromagnetic field generated by the adjacent windings.In other embodiments, the ferrite structure includes an opening in acenter section where the center section is located at a center of thetwo-by-two square pattern and the center section is external to each ofthe four windings.

In some embodiments, the WPT pad apparatus includes a vertical shieldexternal to the ferrite structure positioned to shunt an electromagneticfield radiating in a direction horizontal with the horizontal surface ofthe ferrite structure. In other embodiments, the vertical shieldincludes a metallic structure oriented transverse to the horizontalsurface of the ferrite structure. In other embodiments, the verticalshield has a width where the width is measured in a direction transverseto the horizontal surface of the ferrite structure. The width includesat least a thickness of an edge of the ferrite structure and a thicknessof the winding. In other embodiments, the vertical shield includes anopening at each corner of the ferrite structure.

In some embodiments, the horizontal surface includes a first horizontalsurface and the WPT pad apparatus also includes a horizontal shieldpositioned on a second horizontal surface of the ferrite structure. Thesecond horizontal surface is distal to the first horizontal surface andplanar with the first horizontal surface. In other embodiments, thehorizontal shield includes metallic plate and the horizontal shieldreduces a strength of an electromagnetic field generated by the fourwindings and radiating through the horizontal shield to below aspecified limit. In other embodiments, the ferrite structure isthermally coupled to the horizontal shield where heat generated in eachof the four windings and in the ferrite structure is transmitted to thehorizontal shield. In other embodiments, the WPT pad apparatus includesa vertical shield external to the ferrite structure. The vertical shieldis coupled to the horizontal shield and extending in a directiontransverse to the horizontal shield in a direction of the ferritestructure and the four windings.

In some embodiments, each of the four windings includes a spiral patternstarting at an edge of a winding center section and expanding away fromthe center section. The center section has an area without conductors ata center of a winding. In other embodiments, each winding of the fourwindings includes two or more winding sections wound in parallel andeach winding section is connected to a capacitor located at the centersection of the winding. In other embodiments, the center section of eachwinding includes a ferrite chimney coupled to the horizontal surface ofthe ferrite structure and extending in a direction transverse to thehorizontal surface at least a thickness of the winding associated withthe center section.

In some embodiments, each of the four windings includes a conductorwhere each conductor has multiple strands. The strands are electricallyisolated from each other and the conductor has a wide side and a narrowside. The wide side of the conductor is oriented transverse to thehorizontal surface. In other embodiments, the conductor is a litz wire.

Another WPT pad apparatus includes a ferrite structure and four windingsadjacent to the ferrite structure. A horizontal surface of the ferritestructure is adjacent to each of the four windings. Each of the fourwindings is wound in a horizontal pattern that is planar to thehorizontal surface. The four windings are arranged in a two-by-twosquare pattern in a north-south-north-south polarity arrangement, andfor adjacent windings of the four windings, the ferrite structure has amagnetic pathway. A ferrite pathway between adjacent windings of thefour windings has a thickness and a width to provide a low impedance,unsaturated magnetic pathway for an electromagnetic field generated bythe adjacent windings. The ferrite structure includes an opening in acenter section where the center section is located at a center of thetwo-by-two square pattern and the center section is external to each ofthe four windings.

In some embodiments, the WPT pad apparatus includes a vertical shieldexternal to the ferrite structure positioned to shunt an electromagneticfield radiating in a direction horizontal with the horizontal surface ofthe ferrite structure. In other embodiments, the WPT pad apparatusincludes a ferrite chimney coupled to the horizontal surface of theferrite structure in the center section of each winding and extending ina direction transverse to the horizontal surface at least a thickness ofthe winding associated with the center section.

A WPT system includes a first stage with a resonant converter or analternating current (“AC”) to direct current (“DC”) converter. The firststage is configured to wirelessly transmit power to a second stage on avehicle. The WPT system includes a WPT pad apparatus that receives powerfrom the first stage and transmits power wirelessly to a secondary padof the second stage. The WPT pad apparatus includes a ferrite structureand four windings adjacent to the ferrite structure. A horizontalsurface of the ferrite structure is adjacent to each of the fourwindings, and each of the four windings is wound in a horizontal patternthat is planar to the horizontal surface. The four windings are arrangedin a two-by-two square pattern in a north-south-north-south polarityarrangement.

Another WPT pad apparatus includes a ferrite structure with a horizontalsurface and a winding with a conductor. The conductor has a long sideand a narrow side. The long side is oriented transverse to thehorizontal surface of the ferrite structure and the narrow side isplanar with the horizontal surface. The conductor of the winding iswound in a spiral-type configuration.

In some embodiments, the conductor has a rectangular shape and has twoparallel long side and two parallel narrow sides. In other embodiments,the conductor has multiple strands where the strands are electricallyisolated from each other. In other embodiments, the WPT pad apparatusincludes a winding with one or more winding guides. The winding guidesmaintain the conductor in a winding pattern. In other embodiments, thewinding guides maintain spacing between each turn of the winding. Inother embodiments, the winding structure includes posts and/or channelsthat maintain the conductor in a winding pattern.

A method for constructing a fractional winding for wireless powertransfer includes providing a ferrite structure with a planar surfaceand winding a conductor in a planar arrangement in a spiral-type patternabout a center point. The conductors are arranged to be adjacent to theplanar surface of the ferrite structure. The winding has a startingpoint and each turn of the winding is adjacent to the planar surface ofthe ferrite structure. The winding includes a fractional number of turnswhere the starting point is at a different angle from a radial lineextending radially from the center point than angle of an ending pointof the winding measured from the radial line.

In some embodiments, a length of the conductor relates to an amount ofinductance of the winding and the method includes determining a targetamount of winding inductance and selecting the fractional number ofturns based on the target amount of inductance for the winding. In someembodiments, the inductance of the winding is further related to adiameter of the spiral-type pattern of the winding and the methodincludes determining a diameter of the spiral-type pattern along withselecting the fractional number of turns based on the target amount ofinductance of the winding. In other embodiments, the conductors arewound within a winding structure with channels and/or posts thatmaintain the winding in a particular shape and spacing. The channels aredistributed around the center point at various distances from the centerpoint to provide for various diameters of the spiral-type pattern andthe winding structure has a plurality of gaps between the channelsand/or posts arranged to provide pathways to a center section of thewinding for a fractional number of turns. In other embodiments, themethod includes covering the conductors within the winding structurewith a position maintaining material that maintains the winding in aselected spiral-type pattern with a fractional number of turns, andplacing the winding structure with the conductors adjacent to theferrite structure, where the conductors are adjacent to the planarsurface of the ferrite structure.

A WPT pad includes a horizontal shield, a ferrite structure mounted tothe horizontal shield, where the ferrite structure has a planar surfacedistal to a surface of the ferrite structure mounted to the horizontalshield, and a winding with a conductor in a planar arrangement in aspiral-type pattern about a center point, where the winding has a centersection with the center point within the center section. The WPT padincludes a capacitor located within the center section of the winding, awinding insulator located between conductors of the winding and theferrite structure, where the winding insulator is electricallyinsulating the conductors from the ferrites structure, and a capacitorinsulator located adjacent to the capacitor on a side of the capacitorfacing the horizontal shield. The capacitor insulator includes amaterial that electrically insulates the capacitor from the ferritestructure and/or the horizontal shield. The capacitor insulatortransmits heat from the capacitor to one or more of the horizontalshield and the ferrite structure.

In some embodiments, the capacitor insulator includes a ceramic printedcircuit board (“PCB”) material. In other embodiments, the capacitorinsulator includes aluminum nitride. In other embodiments, the windinginsulator includes a glass-reinforced epoxy laminate. In otherembodiments, the winding insulator has a National ElectricalManufacturers Association (“NEMA”) flame retardant (“FR”) rating of 4(“FR 4”). In other embodiments, the capacitor is secured to thehorizontal shield with a fastener and the fastener is electricallyinsulated from the capacitor with a connector insulator.

In some embodiments, the ferrite structure has a horizontal shield withthe planar surface and a ferrite chimney. The ferrite chimney is locatedin the center section and is adjacent to the winding. The ferritechimney extends in a direction away from the planar surface of theferrite structure to at least a distance of a thickness of theconductors or twice a thickness of the horizontal shield. The thicknessis measured in a direction transverse to the planar surface. The ferritechimney is thermally and electrically coupled to the horizontal shieldof the ferrite structure. In other embodiments, the WPT pad includes awinding structure that separates turns of the winding a specifieddistance. The winding structure is electrically insulating turns of thewinding from each other and maintaining the conductors of the winding inthe spiral-type pattern.

A winding structure for a WPT pad includes a base with an insulatingmaterial and channels within the base and/or one or more posts extendingfrom the base to a height of a top of the channels. The channels andposts are configured to maintain one or more conductors of a winding ina particular shape and spacing. The channels are distributed around acenter point of the winding at various distances from the center pointto provide for various diameters of a spiral-type pattern, and thewinding structure includes a plurality of gaps between the one or morechannels and/or the one or more posts. The plurality of gaps arearranged to provide pathways to a center section of the winding.

In some embodiments, the winding structure includes a capacitor opening.The capacitor opening is sized for one or more capacitors. In otherembodiments, the capacitor opening is located in the center section. Inother embodiments, the winding structure includes one or more ferriteopenings. Each ferrite opening is sized for a ferrite chimney. At leastone ferrite opening is located in the center section at an outerperimeter of the center section and adjacent to the one or moreconductors of the winding. In other embodiments, the winding structureincludes one or more terminal slots and a terminal within each terminalslot. One or more conductors of the winding each terminate on a terminalwithin a terminal slot. The terminal slots have a length longer than aterminal and the terminal of a terminal slot is movable within theterminal slot of the terminal along the length of the terminal slot.

In some embodiments, the winding structure includes a positionmaintaining material placed around components within the windingstructure where the position maintaining material is placed around thecomponents once a configuration of the components is set. In otherembodiments, the position maintaining material is an epoxy resin. Inother embodiments, the winding structure includes nylon.

Another WPT pad includes a ferrite structure, a first winding adjacentto the ferrite structure, where the first winding is arranged in aspiral-type pattern, and a second winding adjacent to the ferritestructure. The second winding is arranged in a spiral-type pattern andthe second winding is wound parallel to the first winding. The first andsecond windings are arranged to compensate for a difference in lengthbetween the first winding and the second winding for portions of thefirst and second windings wound adjacent to each other.

In some embodiments, starting points of the first and second windingsare at an exterior of the first and second windings and the startingpoint of the second winding is before the starting point of the firstwinding and an ending point of the second winding is after an endingpoint of the first winding. In other embodiments, a length of the secondwinding is equal to a length of the first winding. In other embodiments,the starting point of the first winding is positioned so a conductorconnected to the ending point of the second winding and traversing thefirst and second windings to the starting point of the first windingtraverses perpendicular to the first and second windings to reach thestarting point of the first winding, and the starting point of thesecond winding is positioned so a conductor connected to the endingpoint of the second winding and traversing the first and second windingsto the starting point of the second winding traverses perpendicular tothe first and second windings to reach the starting point of the secondwinding.

In some embodiments, the first winding includes a first conductor and afourth conductor and the second winding includes a second conductor anda third conductor. The first conductor is an outermost conductor and isadjacent to the second conductor, the second conductor is adjacent tothe third conductor, and the third conductor is adjacent to the fourthconductor is an innermost conductor. In other embodiments, ending pointsof the first, second, third and fourth conductors are at a centersection of the first and second windings and a starting point of thefirst, second, third and fourth conductors are at an exterior of thefirst and second windings. The ending point of the first conductor isconnected to the starting point of the fourth conductor and the endingpoint of the second conductor is connected to the starting point of thethird conductor. In other embodiments, ending points of the first,second, third and fourth conductors are at a center section of the firstand second windings and a starting point of the first, second, third andfourth conductors are at an exterior of the first and second windings.The ending point of the first conductor is connected to a first terminalof a first capacitor and a second terminal of the first capacitor isconnected to the starting point of the fourth conductor. The endingpoint of the second conductor is connected to a first terminal of asecond capacitor and a second terminal of the second capacitor isconnected to the starting point of the third conductor.

FIG. 1 is a schematic block diagram illustrating one embodiment of a WPTsystem 100 with a low voltage WPT pad. The WPT system 100 includes apower converter apparatus 104 and a secondary receiver apparatus 106separated by a gap 108, and a load 110, which are described below.

The WPT system 100 includes a power converter apparatus 104 thatreceives power from a power source 112 and transmits power over a gap108 to a secondary receiver apparatus 106, which transfers power to aload 110. The power converter apparatus 104, in one embodiment, may becalled a switching power converter and includes a resonant converter 118that receives a direct current (“DC”) voltage from a DC bus 116.

In one embodiment, the power source 112 provides DC power to the DC bus116. In another embodiment, the power source 112 is an alternatingcurrent (“AC”) power source, for example from a building power system,from a utility, from a generator, etc. and the power converter apparatus104 includes a form of rectification to provide DC power to the DC bus116. For example, the rectification may be in the form of a power factorcorrection and rectification circuit 114. In the embodiment, the powerfactor correction and rectification circuit 114 may include an activepower factor correction circuit, such as a switching power converter.The power factor correction and rectification circuit 114 may alsoinclude a full-bridge, a half-bridge rectifier, or other rectificationcircuit that may include diodes, capacitors, surge suppression, etc.

The resonant converter 118 may be controlled by a primary controller120, which may vary parameters within the resonant converter 118, suchas conduction time, conduction angle, duty cycle, switching, etc. Theprimary controller 120 may receive information from sensors and positiondetection 122 within or associated with the power converter apparatus104. The primary controller 120 may also receive information wirelesslyfrom the secondary receiver apparatus 106.

The power converter apparatus 104 includes a primary pad 126 (i.e. aprimary WPT pad) that receives power from the resonant converter 118. Inthe depicted embodiment, the primary pad 126 includes four windings,which may also be termed “pads.” To support the windings, the powerconverter apparatus 104 may include multiple resonant converters 118. Inone embodiment, portions of the resonant converter 118 and primary pad126 form a resonant circuit that enables efficient wireless powertransfer across the gap 108. In another embodiment, the power converterapparatus 104 includes a switching power converter that is not aresonant converter. The gap 108, in some embodiments includes an airgap, but may also may partially or totally include other substances. Forexample, where the primary pad 126 is in a roadway, the gap 108 mayinclude a resin, asphalt, concrete or other material just over thewindings of the primary pad 126 in addition to air, snow, water, etc.between the primary pad 126 and a secondary pad 128 located in thesecondary receiver apparatus 106.

The secondary receiver apparatus 106 includes a secondary pad 128 (i.e.a secondary WPT pad) connected to a secondary circuit 130 that deliverspower to the load 110. In the depicted embodiment, the secondary pad 128may include multiple windings, which may also be termed “pads.” Eachwinding may feed a separate secondary circuit 130. The secondaryreceiver apparatus 106 may also include a secondary decouplingcontroller 132 that controls the secondary circuit 130 and may also bein communication with sensors and/or position detection 136 and wirelesscommunications 134 coupled to the power converter apparatus 104.

In one embodiment, the secondary receiver apparatus 106 and load 110 arepart of a vehicle 140 that receives power from the power converterapparatus 104. The load 110 may include a battery 138, a motor, aresistive load, a circuit or other electrical load. For example, the WPTsystem 100 may transfer power to a portable computer, a consumerelectronic device, to an industrial load, or other portable load thatwould benefit from receiving power wirelessly.

In one embodiment, the secondary circuit 130 includes a portion ofresonant circuit that interacts with the secondary pad 128 and that isdesigned to receive power at a resonant frequency. In anotherembodiment, the secondary circuit 130 includes a power conditioningcircuit that is not a resonant circuit. The secondary circuit 130 mayalso include a rectification circuit, such as a full-bridge rectifier, ahalf-bridge rectifier, and the like. In another embodiment, thesecondary circuit 130 includes a power converter of some type thatreceives power from the resonant circuit/rectifier and actively controlspower to the load 110. For example, the secondary circuit 130 mayinclude a switching power converter. In another embodiment, thesecondary circuit 130 includes passive components and power to the load110 is controlled by adjusting power in the power converter apparatus104. In another embodiment, the secondary circuit 130 includes an activerectifier circuit that may receive and transmit power. One of skill inthe art will recognize other forms of a secondary circuit 130appropriate for receiving power from the secondary pad 128 anddelivering power to the load 110.

The resonant converter 118, in one embodiment, includes an activeswitching section coupled to a resonant circuit formed with componentsof the resonant converter 118 and the primary pad 126. The resonantconverter 118 is described in more detail with regard to FIGS. 2A and2B.

FIG. 2A is a schematic block diagram illustrating one embodiment 200 ofa power converter apparatus 104. The power converter apparatus 104 isconnected to a power source 112 and includes a power factor correctionand rectification circuit 114 connected to a DC bus 116 feeding aresonant converter 118 connected to a primary pad 126 as described withregard to the WPT system 100 of FIG. 1.

The resonant converter 118 includes a switching module 202 and a tuningsection 204. In one embodiment, the switching module 202 includes fourswitches configured to connect the DC bus 116 and to ground. Typically,switches S1 and S3 close while switches S2 and S4 are open andvice-versa. When switches S1 and S3 are closed, the DC bus 116 isconnected to a positive connection of the tuning section 204 throughinductor L1 a and the ground is connected to the negative connection ofthe tuning section 204 through inductor L1 b while switches S2 and S4are open. When switches S2 and S4 are closed, the ground is connected tothe positive terminal of the tuning section 204 and the DC bus 116 isconnected to the positive connection of the tuning section 204. Thus,the switching module alternates connection of the DC bus 116 and groundto the tuning section 204 simulating an AC waveform. The AC waveform istypically imperfect due to harmonics.

Typically, switches S1-S4 are semiconductor switches, such as ametal-oxide-semiconductor field-effect transistor (“MOSFET”), a junctiongate field-effect transistor (“JFET”), a bipolar junction transistor(“BJT”), an insulated-gate bipolar transistor (“IGBT”) or the like.Often the switches S1-S4 include a body diode that conducts when anegative voltage is applied. In some embodiments, the timing of openingand closing switches S1-S4 are varied to achieve various modes ofoperations, such as zero-voltage switching.

The tuning section 204 of the resonant converter 118 and the primary pad126 are designed based on a chosen topology. For example, the resonantconverter 118 and primary pad 126 may form aninductor-capacitor-inductor (“LCL”) load resonant converter, a seriesresonant converter, a parallel resonant converter, and the like. Theembodiment depicted in FIG. 2A includes an LCL load resonant converter.

Resonant converters include an inductance and capacitance that form aresonant frequency. When a switching frequency of the tuning section 204is at or close to the resonant frequency, voltage with the tuningsection 204 and primary pad 126 often increases to voltages levelshigher than the voltage of the DC bus 116. For example, if the voltageof the DC bus 116 is 1 kilovolt (“kV”), voltage in the tuning section204 and resonant converter 118 may be 3 kV or higher. The high voltagesrequire component ratings, insulation ratings, etc. to be high enoughfor expected voltages.

The primary pad 126 includes capacitor C3 and inductor Lp while thetuning section 204 includes series capacitor C2. Capacitors C2 and C3add to provide a particular capacitance that forms a resonant frequencywith inductor Lp. In some embodiments, the power converter apparatus 104includes a single series capacitor in the tuning section 204 or in theprimary pad 126. While FIG. 2A is focused on the resonant converter 118and primary pad 126, the secondary receiver apparatus 106 includes asecondary pad 128 and a secondary circuit 130 that typically includes atuning section 204 where the inductance of the secondary pad 128 andcapacitance of the tuning section 204 of the secondary circuit 130 forma resonant frequency and the secondary pad 128 and secondary circuit 130have voltage issues similar to the primary pad 126 and resonantconverter 118. In other embodiments, the tuning section 204 and primarypad 126 are not designed to produce a resonance, but instead conditionvoltage from the switching module 202. For example, the tuning section204 may filter out harmonic content without filtering a switchingfrequency.

FIG. 2B is a schematic block diagram illustrating one embodiment 201 ofa power converter apparatus 104 with multiple resonant converters 118a-d feeding windings 126 a-d of one or more primary pads 126. FIG. 2B ispresented in a one-line diagram format. One of skill in the art willrecognize that each line between elements represents two or moreconductors. The power source 112, power factor correction andrectification circuit 114 and DC bus 116 are substantially similar tothose described in the embodiment 200 of FIG. 2A. The power converterapparatus 104 includes four resonant converters 118 a-d (generically orindividually “118”) where each resonant converter 118 includes aswitching module 202 and may include a tuning section 204. Each resonantconverter 118 feed a winding (e.g. 126 a) of a primary pad 126, whichmay include multiple windings 126 a-d. A resonant converter (e.g. 118 a)may feed an individual primary pad 126.

FIG. 3A is a schematic block diagram illustrating one embodiment 300 ofa secondary circuit 130 feeding a load 110. A secondary pad 128 feeds atuning section 302 within the secondary circuit 130 and the tuningsection 302 feeds a rectification section 304 in the secondary circuit130, which feeds a load 110.

The secondary pad 128 includes one or more windings arranged to receivepower from a primary pad 126. The secondary pad 128 may include aferrite structure and windings arranged in a pattern that efficientlyreceives power from the primary pad 126. In one embodiment, thesecondary pad 128 mirrors the primary pad 126 transmitting power. Inanother embodiment, the secondary pad 128 differs from the primary pad126. Typically, the secondary pad 128 includes an inductance Ls formedas a result of the windings and the ferrite structure of the secondarypad 128. In one embodiment, the secondary pad 128 includes a capacitorC4.

The tuning section 302 includes one or more capacitors C5, C6 andinductors L2 a, L2 b that are arranged to form a resonant circuit withthe secondary pad 128 with a resonant frequency. In some embodiments,capacitor C6 is not present. In one embodiment, the resonant frequencymatches a resonant frequency of the primary pad 126 transmitting power.Typically, a resonant frequency is formed between the inductor Ls of thesecondary pad 128 and series capacitors C4 and C5 of the secondary pad128 and/or tuning section 302. In some embodiments, the secondary pad128 or the tuning section 302 include a single series capacitor C4 orC5. Other capacitors (e.g. C6) and inductors (e.g. L2 a, L2 b) may forma low pass filter to reduce voltage ripple at the resonant frequency. Inother embodiments, a low-pass filter is included after rectificationelements in the rectification section 304. For example, a capacitor C7may be included. One of skill in the art will recognize otherconfigurations of the tuning section 302 that form a resonant tank withthe secondary pad 128 and pass energy to the rectification section 304or another suitable circuit.

A rectification section 304 includes diodes, switches, or otherrectification elements to convert alternating current (“AC”) power todirect current (“DC”) power. The rectification section 304 depicted inFIG. 3 includes a full bridge rectifier with four diodes D1-D4. In someembodiments, the diodes D1-D4 are replaced with active elements, such asswitches, which may be used to reduce harmonics, reduce powerconsumption, and the like. For example, the rectification section 304may include a switching power converter that controls an output voltageto the load 110.

The load 110, in one embodiment is a battery 138. In other embodiments,the load 110 may include other components, such as a motor, a resistiveload, electronics, and the like. In one embodiment, the secondary pad128, secondary circuit 130 and load 110 are part of a vehicle 140. Inother embodiments, the secondary pad 128, secondary circuit 130 and load110 are part of a computing device, a smartphone, and the like.

FIG. 3B is a schematic block diagram illustrating one embodiment 301 ofseveral windings 128 a-d of a secondary pad 128 feeding severalsecondary circuits 130 a-d, which feed a load 110. The secondarycircuits 130 a-d, in one embodiment, are in an enclosure 306 and feed asecondary DC bus 308, which feeds the load 110. A secondary pad 128 withmultiple windings 128 a-d is advantageous to increase a power level andmultiple windings 128 a-d may also be used in determining alignment.Multi-winding pads 126, 126 are discussed in more detail below.

FIG. 4 is a schematic block diagram illustrating one embodiment of a lowvoltage WPT pad. In the embodiment, the capacitance Cs has beendistributed in five capacitors, Cs1, Cs2, Cs3, Cs4 and Cs5. The windingof the primary pad 126, which forms an inductance, is divided into foursections, Lp1, Lp2, Lp3, Lp4. The capacitors Cs2, Cs3, Cs4 and Cs5 aredistributed between winding sections as depicted. While five capacitorsand four winding sections are depicted, one of skill in the art willrecognize that other numbers of capacitors and winding sections may beused. In addition, the low voltage WPT pad may be for a primary or asecondary pad.

FIG. 5 is a schematic block diagram illustrating one embodiment of a lowvoltage WPT pad with two parallel windings. In the embodiment, thecapacitance Cs has been distributed in two parallel windings. A firstwinding includes three capacitors, Cs1 a, Cs2 a, and Cs3 a. The firstwinding of the primary pad 126, which forms an inductance, is dividedinto two sections, Lp1 a and Lp2 a. In the first winding, capacitors Cs1a, Cs2 a and Cs3 a are distributed between winding sections as depicted.A second parallel winding includes three capacitors, Cs1 b, Cs2 b, andCs3 b. The second winding of the primary pad 126, which forms aninductance, is divided into two sections, Lp1 b and Lp2 b. In the secondwinding, capacitors Cs1 b, Cs2 b and Cs3 b are distributed betweenwinding sections as depicted. While six capacitors and four windingsections are depicted, one of skill in the art will recognize that othernumbers of capacitors and winding sections may be used. In addition,while the windings are depicted connected in parallel, in otherembodiments each winding may be fed by a separate resonant converter118. In another embodiment, the windings are connected in series. Thelow voltage WPT pad may be for a primary or a secondary pad.

FIG. 6 is a schematic block diagram illustrating one embodiment 600 of aWPT pad 126, 128 with four windings 602 a, 602 b, 602 c, 602 d(generically or collectively “602”) with a ferrite structure removed.Each winding 602 is configured similar to the windings depicted in FIG.5 with capacitors Cs1 a, Cs2 a and Cs3 a on one winding and Cs1 b, Cs2 band Cs3 b on the other winding, but other configurations are alsocontemplated, such as the embodiment 400 of FIG. 4, windings 602 withoutintervening capacitors, etc. and the ferrite structure, verticalshields, horizontal shields, four windings 602 in a two-by-two pattern,etc. described below are applicable to the various windingconfigurations. The conductors 604 in the windings 602 are depicted aslines where the inductances (i.e. Ls1 a) are not called outspecifically. Each winding 602 includes a ferrite chimney 606, which isa ferrite section adjacent to the conductors 604 of the windings 602.The ferrite chimney 606 is described in more detail with regard to FIG.8. Connection points 608 are depicted as square boxes. Each winding 60a, 602 b, 602 c, 602 d is configured the same so for clarity only thefirst winding 602 a is labeled.

The four windings 602 are surrounded by vertical shields 610. Eachvertical shield 610 is located external to the ferrite structure and ispositioned to shunt an electromagnetic field radiating in a directionhorizontal with a horizontal surface of the ferrite structure. Thevertical shields 610 are described more in relation to FIGS. 7 and 8.

In one embodiment, each of the four windings 602 a-d is wound in aspiral pattern starting at an edge of a winding center section andexpanding away from the center section. The center section is an areawithout conductors at a center of a winding (e.g. 602 a). In oneembodiment, the spiral is an Archimedean spiral. In another embodiment,the spiral is a modified Archimedean spiral that is not purely circular,but includes straight sections or other modifications to accommodate theferrite chimneys 606, convenience, etc.

FIG. 7 is a schematic block diagram illustrating the embodiment 600 ofthe WPT pad 126, 128 with four windings 602 with a ferrite structure 702a, 702 b, 702 c, 702 d (generically or collectively “702”) included foreach winding 602 a, 602 b, 602 c, 602 d. The four windings 602 a-d areadjacent to the ferrite structure 702, where a horizontal surface of theferrite structure 702 is adjacent to each of the four windings 602a-d.Each of the four windings 602 a-d are wound in a horizontal pattern thatis planar to the horizontal surface. The four windings 602 a-d arearranged in a two-by-two square pattern in a north-south-north-southpolarity arrangement.

The ferrite structure 702 a of the first winding 602 a is configured tomagnetically connect to the ferrite structure 702 b, 702 d of eachadjacent winding 602 b, 602 d to create a low impedance magnetic pathwaybetween each winding 602. In one embodiment, the ferrite pathway betweenadjacent windings (e.g. 602 a, 602 b) of the four windings 602 has athickness and a width to provide a low impedance, unsaturated magneticpathway for an electromagnetic field generated by the adjacent windings602 a, 602 b. For example, the ferrite structure 702 may be sized for anamount of power wirelessly transferred through the WPT pad 126, 128 tonot saturate for an expected electromagnetic field generated by thewindings 602.

In one embodiment, the resultant ferrite structure 702 includes fourseparate ferrite structures 702 a-d that are positioned to be adjacentto allow for a low impedance magnetic pathway from one winding (e.g. 602a) to another winding (e.g. 602 b). For example, the ferrite structures702 a-d may be touching or are positioned very close to each other. Inanother embodiment, the ferrite structure 702 is constructed to be aunitary structure. The ferrite structure 702 may be a single piece offerrite or may be constructed of ferrite blocks or similar ferritepieces.

In one embodiment, the resultant ferrite structure 702 includes anopening in a center section 704, where the center section 704 is locatedat a center of the two-by-two square pattern of windings 602 and thecenter section is external to each of the four windings 602 a-d.Typically, having an opening in the center section 704 is more costeffective than ferrite placed in the center section 704. Having ferritein the center section 704 may provide little benefit compared to a costof the ferrite. In another embodiment, the center section 704 includesferrite.

The embodiment 600 includes vertical shields 610 external to the ferritestructure 702 positioned to shunt an electromagnetic field radiating ina direction horizontal with a horizontal surface of the ferritestructure 702. In one embodiment, the vertical shield 610 includes ametallic plate oriented transverse to the horizontal surface of theferrite structure 702. In another embodiment, the vertical shield 610has an opening 706 at each corner of the windings 602 a-d and/or ferritestructure 702, as depicted. As depicted, the vertical shields 610 mayrun along only a part of an edge of the windings 602.

External to each winding in FIGS. 6 and 7 is a winding structure 612that may be used to support the windings, ferrite chimneys 606,connection points 608, etc. In some embodiments, the winding structure612 is non-magnetic. In some embodiments, the winding structure 612 isrigid and includes channels, ridges, indentations, etc. to supportvarious components of the windings 602. In some embodiments, the windingstructure 612 provides insulation between components and has adielectric breakdown sufficient for voltages anticipated on the primarypad 126 or secondary pad 128. In some embodiments, the winding structure612 is a rigid material, such as nylon. In one embodiment, an insulatinglayer (not shown) is placed between the windings 602 and the ferritestructure 702. For example, the insulating layer may meet the FR-4standard of the National Electrical Manufacturers Association (“NEMA”)LI 1-1998 specification, and may be a glass-reinforced epoxy laminate orother similar material.

In one embodiment, the windings 602 each include conductors 604 whichinclude multiple strands. In one embodiment, each strand of a conductor604 is electrically isolated from other strands within the conductor604, for example, to minimize skin effect. In some embodiments, theconductors 604 are a litz wire. In other embodiments, the conductors 604are not litz wire, but are in other configurations. For example, theconductor 604 may include one or more strands of copper or otherconductive metal configured to reduce skin effect and may be configuredto be pliable. The litz wire, in one embodiment, includes fine strandsof conductors and some of the strands may be wound and/or woventogether. In one embodiment, the litz wire is rectangular shaped with awide side and a narrow side. The litz wire may bend more readily in adirection transverse to the wide side. In one embodiment, the wide sideof the litz wire is oriented transverse to a horizontal surface of theferrite structure 702, which may facilitate tighter bends than if thelitz wire was oriented with the wide side toward the horizontal surfaceof the ferrite structure 702. The litz wire, in one embodiment, isplaced in channels in the winding structure 612 to maintain a particularpattern, spacing, etc. In another embodiment, the winding structure 612includes extensions, posts, guides, or the like to facilitate aparticular pattern, spacing, etc. of the litz wire.

In one embodiment, the vertical shields 610 are adjacent to and/orconnected to a horizontal shield (not shown), which is located adjacentto the ferrite structure 702 where the ferrite structure 702 is betweenthe horizontal shield and the windings 602. In another embodiment, thevertical shield 610 is coupled to the horizontal shield. In anotherembodiment, the vertical shield 610 is adjacent to the horizontal shieldbut is not coupled to the horizontal shield. In one embodiment, thehorizontal shield extends beyond the ferrite structure 702 and thewindings 602 and may be placed between the ferrite structure 702 and avehicle 140 for a secondary pad 128 or between the ferrite structure 702and a ground below a primary pad 126. In one embodiment, the horizontalshield is thermally and/or electrically coupled to the ferrite structure702. The horizontal shield may be a single structure or may be splitinto multiple horizontal shields, for example a horizontal shield 708for each winding 602 a-d. A horizontal shield that is a single plate maybe advantageous to prevent water or another substance from passingbeyond the horizontal shield to the ferrite structure 702 and/orwindings 602. The horizontal shield is described in more detail withregard to the embodiment 800 of FIG. 8.

FIG. 8 is a schematic block diagram illustrating one embodiment 800 of across section of a primary pad 126 and a secondary pad 128, each with aferrite chimney 606 and a vertical shield 610. The embodiment 800 issubstantially similar to the embodiment 600 depicted in FIGS. 6 and 7.

Each of the primary pad 126 and secondary pad 128 include a horizontalshield 802 with a vertical shield 610 on an end of the horizontal shield802. In the embodiment 800, the ferrite structure 702 and conductors 604of the windings 602 are separated from the vertical shields 610. Inanother embodiment, the vertical shields 610 are adjacent to the ferritestructure 702 and/or conductors 604. For example, the vertical shields610 may be placed within sides of a vehicle 140 to minimize strayelectromagnetic field beyond the vehicle 140 where people may bestanding.

A width (measured from the horizontal shield 802 in a directiontransverse to the horizontal shield 802), a thickness, and a material ofthe vertical shield 610 may be chosen along with a position of thevertical shields to maintain an electromagnetic field strength below aspecified limit where people are located, such as a governmentalstandard. In addition, the thickness, size, and material of thehorizontal shield 802 may be chosen to reduce an electromagnetic fieldstrength below a specified limit where people are located. In oneembodiment, the vertical shield 610 and/or the horizontal shield 802include a metallic material, such as aluminum. One of skill in the artwill recognize other metallic materials suitable for the vertical shield610 and/or the horizontal shield 802.

In one embodiment, the primary pad 126 and secondary pad 128 eachinclude a ferrite chimney 606. The ferrite chimneys 606 may reduce adistance between the pads 126, 128 and may provide a convenient magneticpathway 804 between the pads 126, 128. The ferrite chimneys 606, in oneembodiment, extend at least to a distance away from the ferritestructure 702 that is at least level with the conductors 604 of thewindings 602 and may extend beyond the conductors 604, as depicted inFIG. 8. In another embodiment, the ferrite chimneys 606 extend at leastto a distance away from the ferrite structure 702 that is at least twicea thickness of the horizontal shield 802. In one embodiment, the ferritechimneys 606 surround a center section, which may include capacitors(e.g. Cs2 a, Cs3 a, Cs2 b, Cs3 b). Note that the capacitors Cs2 a, Cs3a, Cs2 b, Cs3 b are not shown for clarity, but are intended to beincluded in the embodiment 800. In another embodiment, the centersection is empty.

The ferrite chimneys 606 are discussed in more detail in U.S. PatentApplication No. 62/554,950 filed Sep. 9, 2017 for Patrice Lethellier,which is incorporated herein by reference for all purposes. In anotherembodiment, the primary pad 126 includes a pyramid-shaped ferritechimney (not shown) that is located at a center of each winding, whichallows for a degree of misalignment between the pads 126, 128 whilemaintaining an adequate degree of magnetic coupling. Pyramid-shapedferrite chimneys are discussed in more detail in U.S. Patent ApplicationNo. 62/554,960 filed Sep. 9, 2017 for Patrice Lethellier, which isincorporated herein by reference for all purposes.

North (“N”) and south (“S”) poles are depicted as well as a magneticpathway 804 where electromagnetic flux may travel from north to southpoles and then through the ferrite structure 702. The ferrite structure702 extending between windings provides a low impedance magnetic pathwayfrom one winding (e.g. 602 a) to another winding (e.g. 602 b, 602 d),which facilitates efficient transfer of energy wirelessly between thepads 126, 128. In addition, each winding 602 a-d may be connected to adifferent resonant converter 118 to parallel the resonant converters 118to increase the wireless power transfer capability of the pads 126, 128.The magnetic pathway formed in the ferrite structure 702 and the ferritechimneys 606, as depicted in FIGS. 7 and 8, help to direct theelectromagnetic field generated in the windings 602 into the ferritestructure 702 and to minimize stray electromagnetic field external tothe ferrite structure 702, ferrite chimneys 606 and area directlybetween the ferrite chimneys 606, i.e. in locations where theelectromagnetic field is not wanted. In addition, the horizontal shields802 and the vertical shields 610 help to shunt stray electromagneticfields to minimize electromagnetic field strength beyond the horizontalshields 802 and the vertical shields 610.

FIG. 9 is a schematic block diagram illustrating one embodiment 900 of asimplified ferrite structure 902 of a four winding WPT pad (e.g. 126,128) and vertical shields 610 depicting shunting of a strayelectromagnetic field. The simplified ferrite structure 902 mayrepresent the ferrite structure of the embodiments 600, 800 of FIGS. 7and 8, but is simply depicted to indicate functionality of the verticalshields 610. The simplified ferrite structure 902 include centersections 904 with north (“N”) and south (“S”) poles as indicated. Strayelectromagnetic field lines 906 extend beyond the simplified ferritestructure 902, but are shunted by the vertical shields 610, as depictedby the field lines 908 in the vertical shields 610. The shunting of thestray electromagnetic field 906 reduces electromagnetic field strengthbeyond the vertical shields 610.

FIG. 10 is a schematic block diagram illustrating one embodiment 1000 ofa center section of a winding 602 with capacitors (e.g. Cs2 a). Theembodiment 1000, in one example, is an enlargement of the center sectionof the embodiment 800 of FIG. 8. In the embodiment 1000, a primary pad126 and secondary pad 128 are depicted and the horizontal shield 802,the ferrite structure 702 with a horizontal surface 1012, the conductors604 of the windings 602, the ferrite chimneys 606 and the capacitors Cs2a, Cs2 b, Cs3 a, Cs3 b (collectively “Cs”) are substantially similar tothose described above in relation to the embodiments 600, 800 of FIGS.6-8.

The capacitors Cs are depicted in the center section of the secondarypad 128 and not in the center section of the primary pad 126. In someembodiments, capacitors Cs of the primary pad 126 may be locatedseparate from the primary pad 126, for example, to avoid replacement ofthe primary pad 126 when a capacitor Cs is replaced. In otherembodiments, the primary pad 126 may include capacitors (e.g. C1, C2 inthe tuning section 204 without capacitors Cs included with the primarypad 126. In other embodiments, the primary pad 126 includes one or morecapacitors Cs in the center section.

In one embodiment, an insulator 1002 that is thermally conductive ispositioned between the ferrite structure 702 and the conductors 604. Theinsulator 1002 provides electrical insulation between the conductors 604and the ferrite structure 702. The insulator 1002 is thermallyconductive to transmit heat from the conductors 604 to the ferritestructure 702, which transmits heat to the horizontal shield 802. Theinsulator 1002, in one embodiment, is FR-4 compliant.

In another embodiment, the capacitors Cs are separated from thehorizontal shield 802 with a spacer 1004. In one embodiment, the spacer1004 is thermally conductive. In another embodiment, the spacer 1004provides electrical insulation between the capacitors Cs and thehorizontal shield 802. In one example, the spacer 1004 includes aluminumnitride, which has a high thermal conductance while including a highresistivity, which provides an insulating property. In otherembodiments, the spacer 1004 is made of beryllium oxide or boronnitride. In one embodiment, the spacer 1004 has a higher thermalconductivity than the insulator 1002. Typically, aluminum nitride orother ceramics provide a higher thermal conductance than FR-4. However,the insulator 1002 is typically spread over a larger area and FR-4 ismore forgiving than ceramics, such as aluminum nitride. Where thermalrequirements increase for the conductors 604, aluminum nitride oranother high thermal conductivity insulator may be used.

The capacitors Cs, in one embodiment are secured to the horizontalshield 802 with a fastener 1006, such as a bolt, screw, rivet, etc. Inone embodiment, the fastener 1006 is separated from the capacitor Cswith an insulating material 1008, which electrically isolates thecapacitor Cs from the fastener 1006. A bus or other conductor (notshown) may connect to the capacitors Cs to a winding 602 or othercomponent in the secondary pad 128.

In one embodiment, the conductors 604 and ferrite chimneys 606 areseparated by winding guides 1010. In one embodiment, the winding guides1010 are part of the winding structure 612. For example, the windingstructure 612 may have channels and/or posts that maintain spacingbetween conductors 604, turns of a conductor 604, the ferrite chimneys606, etc. In another embodiment, the winding guides 1010 are aninsulating material that provides electrical insulation for conductors604, ferrite chimneys 606, etc. sufficient for an expected voltage. Forexample, the winding guides 1010 may be rated for a voltage much higherthan an expected voltage by a certain amount or ratio (i.e. 2 times). Insome embodiments, the winding guides 1010 and/or winding structure 612are nylon or an equivalent material. Nylon may be useful in that nylonmay be formed in a particular shape and typically provide an adequateamount of electrical insulation for a desired thickness.

In one embodiment, a WPT pad 600 includes a ferrite structure 702 with ahorizontal surface 1012 with a winding 602 with a conductor 604 wherethe conductor 604 includes a long side 1014 and a narrow side 1016. Thelong side 1014 is oriented transverse to the horizontal surface 1012 ofthe ferrite structure 702 and the narrow side 1016 is planar with thehorizontal surface 1012. The conductor 604 of the winding 602 is woundin a spiral-type configuration. For example, the conductor 604 may be ina rectangular shape with two parallel long sides 1014 and two parallelnarrow sides 1016, as depicted in FIG. 10. Having a rectangular shapewith the conductor 604 oriented as depicted may facilitate bending ofthe conductor 604 in a direction around the center section 704 of thewinding 602 with a smaller radius than conductors 604 of other shapes,such as a round conductor, a square conductor, etc.

In another embodiment, the conductor 604 is made of litz wire or thelike. The litz wire conductor 604 may include strands and/or sub-strandsof small diameter conductors so that the conductor 604 is made up of alot of conductors with radii much, much smaller than dimensions of theconductor 604. One of skill in the art will recognize properties of alitz wire. The litz wire conductor 604 may also provide additionalpliability to reduce a bending radius around the center section 704 ofthe winding 602. In addition, having the narrow sides 1016 facing theferrite structure 702 also contributes to a more compact winding 602because the conductors 604 may be packed together closer than roundconductors, square conductors, etc.

In one embodiment, the WPT pad 126, 128 includes a winding structure 612with one or more winding guides 1010 where the winding guides 1010maintain the conductor 604 in a winding pattern. (A horizontal portionof the winding structure 612 is not depicted for clarity.) For example,the winding guides 1010 may maintain spacing between each turn of thewinding 602. In another example, the winding structure 612 includesposts and/or channels that maintain the conductor 604 in a windingpattern. The winding structure 612 is described in more detail withregard to FIG. 11.

FIG. 11 is a schematic block diagram illustrating one embodiment of awinding structure 612 that guides conductors 604 within a winding 602.The winding structure 612, in one embodiment, provides a framework forcreating a winding 602 where the winding 602 may have various radii,various number of turns, etc. In one embodiment, the winding structure612 may be used to test various spiral-type winding patterns of one ormore conductors 604 to adjust inductance, number of turns, connection tocomponents, such as capacitors (e.g. Cs), connectors, etc.

In one embodiment, the winding structure 612 includes a base 1102 thatincludes an insulating material. For example, the base 1102 may have aplanar shape and may have channels 1104 and posts 1106 configured tomaintain one or more conductors 604 of a winding 602 in a particularshape and spacing. The winding structure 612 depicted in FIG. 11includes channels 1104 and posts 1106 that may be used to produce awinding 602 in a spiral-type pattern with curved sections and straightsections. For convenience, the channels 1104 are depicted as solid lineswhere conductors 604 (dashed lines) are between the solid lines in thechannels 1104. The solid lines may represent tops of winding guides 1010depicted in FIG. 10 where the channels 1104 are between the windingguides 1010, depicted as the solid lines. The channels 1104 aredistributed around a center point 1108 of the winding 602 at variousdistances from the center point 1108 to provide for various diameters ofa spiral-type pattern.

The channels 1104, in one embodiment, are cut into the base 1102.Material around the posts 1106 expose the posts 1106, which are depictedas short, solid lines. Conductors 604 can follow a channel 1104 andtraverse in a straight line through the posts 1106, for example asdepicted on the bottom, left and top of the winding 602, and cantransition through gaps around the posts 1106 to a different channel1104 or to the center section 1110, for example to capacitors orconnectors. The gaps around the posts 1106 and channels 1104 arearranged to provide pathways to a center section 1110.

The base 1102 includes, in one embodiment, recesses for variouscomponents. In one embodiment, the base 1102 includes capacitoropenings, such as a capacitor opening for capacitors Cs in the centersection 1110 or a capacitor opening 1114 around the perimeter of thewinding 602. The base may also include ferrite openings 1112 for theferrite chimneys 606. For example, the ferrite openings 1112 for theferrite chimneys 606 may be positioned around the center section 1110and may be sized for the ferrite chimneys 606.

In one embodiment, the winding structure 612 includes one or moreterminal slots 1118 and a terminal 1116 within a terminal slot 1118. Oneor more conductors 604 of the winding 602 each terminate on a terminal1116 within a terminal slot 1118. The terminal slots 1118 have a lengthlonger than a terminal 1116 and the terminal 1116 of a terminal slot1118 is movable within the terminal slot 1118 of the terminal 1116 alongthe length of the terminal slot 1118. The terminal 1116 may allow for atransition between a channel 1104 and a portion of a conductor 604traversing the channels 1104 to a capacitor Cs or other component in thecenter section 1110. The terminal slot 1118 allows for the terminal 1116to be easily moved to another position. The winding structure 612 mayalso include one or more fasteners 1120 where the conductor(s) 604terminate on the fasteners 1120. The fasteners 1120 allow for externalconnection of the winding 602.

In one embodiment, the winding structure 612 includes a positionmaintaining material (not shown) placed around components within thewinding structure 612. The position maintaining material is placedaround the components once a configuration of the components is set tomaintain the conductors 604, capacitors Cs, etc. In one embodiment, theposition maintaining material is an epoxy resin. The winding structure612 is advantageous to provide numerous winding configurations andcomponent configurations. For example, a single winding structure 612may be used for several winding designs. Once a winding design is setand the conductors 604 and components are in place, the positionmaintaining material can fill in gaps of the winding structure 612.

FIG. 12 is a schematic block diagram illustrating one embodiment of afractional winding 1200. The fractional winding 1200 includes aconductor 1202 that is capable of terminating at various location in acenter section 1110. For example, the conductor 1202 may terminate atthe top of the center section 1110 with an end 1204 extending to thecenter section 1110, providing 5-¼ turns. In another embodiment, theconductor 1202 may extend (see dashed conductor 1206 and end 1208) tothe right side of the center section 1110 providing 5-½ turns. Inanother embodiment, the conductor 1202 may extend (see dashed conductorwith one dot 1210 and end 1212) to the bottom of the center section 1110providing 5-¾ turns. In another embodiment, the conductor 1202 mayextend (see dashed conductor and two dots 1214 and end 1216) to the leftside of the center section 1110 providing 6 turns. While FIG. 12 depictsa single conductor 1202, the fractional winding 1200 may includeadditional conductors 1202 wound in parallel, as depicted in FIGS. 5 and6. Each conductor 1202, in one embodiment, has a different startingpoint 1218.

The fractional winding 1200 may be used in a WPT pad with a ferritestructure 702 with a horizontal surface 1012. A method for constructinga fractional winding 1200 for wireless power transfer includes providingthe ferrite structure 702 with a horizontal surface 1012 and winding aconductor 1202 in a planar arrangement in a spiral-type pattern about acenter point 1108. The conductor 1202 is arranged to be adjacent to thehorizontal surface 1012 of the ferrite structure 702. The conductor 1202includes a starting point 1218. Each turn of the conductor 1202 isadjacent to the horizontal surface 1012 of the ferrite structure 702,and the fractional winding 1200 includes a fractional number of turnswhere the starting point 1218 is at a different angle from a radial line1220 extending radially from the center point 1108 than angle of anending point (e.g. 1204, 1208, 1212) of the fractional winding 1200measured from the radial line 1220.

A length of the conductor 1202 relates to an amount of inductance of thewinding and the method, in one embodiment, includes determining a targetamount of winding inductance and selecting the fractional number ofturns based on the target amount of inductance for the fractionalwinding 1200. For example, the target inductance may be selected toachieve a desired amount of gain, a resonant frequency, to optimizepower transfer, etc. The target inductance, in some embodiments,includes selecting an inductance value that helps to minimize othercomponents while achieving resonance. One of skill in the art willrecognize other ways to choose a target inductance.

In one embodiment, the inductance of the fractional winding 1200 isrelated to a diameter of the spiral-type pattern of the fractionalwinding 1200 and the method includes determining a diameter of thespiral-type pattern along with selecting the fractional number of turnsbased on the target amount of inductance of the fractional winding 1200.For example, the winding structure 612 of FIG. 11 may be used to adjustthe diameter of the spiral-type pattern and/or to determine atermination point, resulting in a fractional number of turns.

In another embodiment, the conductor 1202 is wound within a windingstructure 612 with one or more of channels 1104 and posts 1106 thatmaintain the fractional winding 1200 in a particular shape and spacing.The channels 1104 are distributed around the center point 1108 atvarious distances from the center point 1108 to provide for variousdiameters of the spiral-type pattern. The winding structure 612 mayinclude a plurality of gaps between the channels 1104 and/or posts 1106arranged to provide pathways to the center section 1110 of thefractional winding 1200 for a fractional number of turns.

The method, in one embodiment, also includes covering the conductorswithin the winding structure with a position maintaining material thatmaintains the fractional winding 1200 in a selected spiral-type patternwith a fractional number of turns, and placing the winding structure 612with the conductors 1202 adjacent to the ferrite structure 702, wherethe conductors 1202 are adjacent to the horizontal surface 1012 of theferrite structure 702.

FIG. 13A is a schematic block diagram illustrating one embodiment of awinding 1300 with four conductors 1302, 1304, 1306, 1308 in parallelconnected to compensate for a variation in winding length. Windings inparallel may differ in inductance 5 percent or more, which candramatically affect power sharing between the windings. Where theconductors 1302, 1304, 1306, 1308 start and terminate at a same angle or(i.e. have a same number of turns, where the “same angle” can be exactor approximate), the first conductor 1302 may be longer than the secondconductor 1304, which may be longer than the third conductor 1306, whichmay be longer than the fourth conductor 1308. The same is true for twowindings in parallel where the first winding may be longer than thesecond winding.

The first and second windings may be arranged to compensate for adifference in length between the first winding and the second windingfor portions of the first and second windings wound adjacent to eachother. Various methods may be used to compensate for differences inlength between conductors, which are discussed with regard to FIGS.13A-D and 14. As used herein, a starting point of a conductor or awinding is located on an exterior of the winding and an ending point ofa conductor or a winding is located in a center section of the winding.

For the winding 1300, connecting the first conductor 1302, i.e. thelongest conductor, and the fourth conductor 1308, i.e. the shortestconductor, while connecting the second conductor 1304 and thirdconductor 1306, which are mid-length conductors, variation in inductancebetween the paralleled first and fourth conductors 1302, 1308 and theparalleled second and third conductors 1304, 1306 may be minimized.

In the depicted embodiment, a capacitor (i.e. 1310, 1312) is connectedat a midpoint of a winding to reduce voltage so the ending point of thefirst conductor 1302 connects to a terminal of a first capacitor 1310and a second terminal of the first capacitor 1310 connects to thestarting point of the fourth conductor 1308. A conductor jumps outacross the conductors 1302-1308 to the starting point of the fourthconductor 1308. At ending points of the third conductor 1306 and at theending point of fourth conductor 1308, a conductor jumps across theconductors 1302-1308 for an external connection.

Current differences between paralleled conductors (e.g. the firstconductor 1302 and the fourth conductor 1308) may also be minimized byincluding a transformer 1314 with a ferrite core and an equal number ofturns. Minimizing an inductance difference between the paralleledconductors (i.e. 1302 and 1308 vs. 1304 and 1308) helps to maintainequal current as well, which is desirable to prevent a conductor (e.g.1308) from carrying more load than other conductors (e.g. 1302, 1304,1306) in the winding 1300. In the depicted embodiment, a current sharingtransformer 1314 connects conductors 1318, 1320 to the starting pointsof the first conductor 1302 and the second conductor 1304. In addition,another current sharing transformer 1316 connects conductors 1322, 1324to the ending points of the third conductor 1306 and the fourthconductor 1308. In some embodiments, the second transformer 1316 is notincluded. In some embodiments, one or more current sharing transformers1314, 1316 are located adjacent to the winding 1300. In otherembodiments, one or more current sharing transformers 1314, 1316 arelocated adjacent to the tuning section 204 where a cable is between thetuning section 204 and the winding 1300. Current sharing conductors arediscussed in more detail in U.S. Provisional Patent No. 62/567,106,filed Oct. 2, 2017 for Patrice Lethellier, which is incorporated hereinby reference for all purposes.

FIG. 13B is a simplified schematic block diagram illustrating thewinding 1300 of FIG. 13A. The simplified diagram includes the conductors1302, 1304, 1306, 1308 depicted as inductors, which represent inductanceof the conductors 1302, 1304, 1306, 1308. The inductors 1302, 1304,1306, 1308 typically differ based on conductor length, geometricvariations, etc.

FIG. 13C is a schematic block diagram illustrating one embodiment of awinding 1301 with four conductors 1302-1308 in parallel connected tocompensate for a variation in winding length. FIG. 13D is a simplifiedschematic block diagram illustrating the winding 1301 of FIG. 13C. Thewinding 1301 in FIGS. 13C and 13D is the same as the winding 1300 inFIGS. 13A and 13B, except without capacitors 1310, 1312. Instead, aconductor connected to the ending point of the first conductor 1302 isconnected to the starting point of the fourth conductor 1308 and theending point of the second conductor 1304 is connected to the startingpoint of the third conductor 1306.

FIG. 14 is a schematic block diagram illustrating one embodiment of awinding 1400 of a WPT pad with two windings 1402 in parallel which areconnected to compensate for a variation in winding length where windingstarting points 1406, 1408 and ending points 1410, 1412 are adjusted tocompensate for length variations. The starting point 1408 of the secondwinding 1404 is before the starting point 1406 of the first winding1402. For example, as seen in FIG. 14, in tracing the first and secondwindings 1402, 1404 radially in a clockwise direction, the startingpoint 1408 of the second winding 1404 starts first and then movingclockwise radially an additional amount, then the starting point 1406 ofthe first winding 1402 is located past the starting point 1408 of thesecond winding 1404.

In addition, an ending point 1412 of the second winding 1404 is after anending point 1410 of the first winding 1402. Again, tracing the firstand second windings 1402, 1404 radially in a clockwise direction, thefirst winding 1402 ends at the ending point 1410, and continuingclockwise radially, the second winding 1404 ends at its ending point1412 after the ending point 1410 of the first winding 1402. A spacing1414 between the starting and ending points 1406-1412 of the windings1402, 1404 is adjusted to compensate for the length discrepanciesbetween the first and second windings 1402, 1404 caused by thepositioning of the first winding 1402 outside the second winding 1404.In one embodiment, the spacing 1414 is adjusted so that a length of thesecond winding 1404 is equal to a length of the first winding 1402. Asused herein, the length of the second winding 1404 being equal to alength of the first winding 1402 includes exactly equal as well asapproximately equal. For example, a difference in length between thefirst winding 1402 and the second winding 1404 may differ one percent orless. In other embodiments, a difference in length between the firstwinding 1402 and the second winding 1404 may differ 0.5 percent or less.While the winding 1400 is depicted in a square pattern, other patternsmay be used and the starting points 1406, 1408 and ending points 1410,1412 may be adjusted accordingly so the first and second windings 1402,1404 are equal or approximately equal in length. Where the winding 1400is in a circular pattern, the spacing 1414 may be measured radially.

In one embodiment, the starting point 1406 of the first winding 1402 ispositioned so a conductor connected to the ending point 1412 of thesecond winding 1404 and traversing the first and second windings 1402,1404 to the starting point 1406 of the first winding 1404 traversesperpendicular to the first and second windings 1402, 1404 to reach thestarting point 1406 of the first winding 1402. A conductor traversingperpendicular, as used herein includes a conductor traversing exactlyperpendicular and a conductor traversing approximately perpendicular.For example, approximately perpendicular includes traversing at an anglein a range of 80 degrees to 90 degrees and may include a range ofbetween 88 degrees and 90 degrees.

In another embodiment, the starting point 1408 of the second winding1404 is positioned so a conductor connected to the ending point 1410 ofthe first winding 1402 and traversing the first and second windings1402, 1404 to the starting point 1408 of the second winding 1404traverses perpendicular to the first and second windings 1402, 1404 toreach the starting point 1408 of the second winding 1404.

In one embodiment, the conductors 1416 from the starting point 1406 thefirst winding 1402 and the ending point 1412 of the second winding 1404are run in close proximity to a cable 1420 to minimize electromagneticradiation. The conductors 1416, in one embodiment, are twisted together.Likewise, in another embodiment, the conductors 1418 from the startingpoint 1408 the second winding 1404 and the ending point 1410 of thefirst winding 1402 are run in close proximity to the cable 1420 tominimize electromagnetic radiation. The conductors 1416, 1418 may bearranged in the cable 1420 to minimize electromagnetic radiation aswell.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A wireless power transfer (“WPT”) pad apparatuscomprising: a ferrite structure; and four windings adjacent to theferrite structure, wherein a horizontal surface of the ferrite structureis adjacent to each of the four windings, each of the four windingswound in a horizontal pattern that is planar to the horizontal surface,wherein the four windings are arranged in a two-by-two square pattern ina north-south-north-south polarity arrangement.
 2. The WPT pad apparatusof claim 1, wherein for adjacent windings of the four windings, theferrite structure comprises a magnetic pathway.
 3. The WPT pad apparatusof claim 2, wherein a ferrite pathway between adjacent windings of thefour windings comprises a thickness and a width to provide a lowimpedance, unsaturated magnetic pathway for an electromagnetic fieldgenerated by the adjacent windings.
 4. The WPT pad apparatus of claim 1,wherein the ferrite structure comprises an opening in a center section,wherein the center section is located at a center of the two-by-twosquare pattern and the center section is external to each of the fourwindings.
 5. The WPT pad apparatus of claim 1, further comprising avertical shield external to the ferrite structure positioned to shunt anelectromagnetic field radiating in a direction horizontal with thehorizontal surface of the ferrite structure.
 6. The WPT pad apparatus ofclaim 5, wherein the vertical shield comprises a metallic structureoriented transverse to the horizontal surface of the ferrite structure.7. The WPT pad apparatus of claim 5, wherein the vertical shieldcomprises a width, the width measured in a direction transverse to thehorizontal surface of the ferrite structure, wherein the width comprisesat least a thickness of an edge of the ferrite structure and a thicknessof the winding.
 8. The WPT pad apparatus of claim 5, wherein thevertical shield comprises an opening at each corner of the ferritestructure.
 9. The WPT pad apparatus of claim 1, wherein the horizontalsurface comprises a first horizontal surface and further comprising ahorizontal shield positioned on a second horizontal surface of theferrite structure, the second horizontal surface distal to the firsthorizontal surface and planar with the first horizontal surface.
 10. TheWPT pad apparatus of claim 9, wherein the horizontal shield comprisesmetallic plate and the horizontal shield reduces a strength of anelectromagnetic field generated by the four windings and radiatingthrough the horizontal shield to below a specified limit.
 11. The WPTpad apparatus of claim 9, wherein the ferrite structure is thermallycoupled to the horizontal shield, wherein heat generated in each of thefour windings and in the ferrite structure is transmitted to thehorizontal shield.
 12. The WPT pad apparatus of claim 9, furthercomprising a vertical shield external to the ferrite structure, thevertical shield coupled to the horizontal shield and extending in adirection transverse to the horizontal shield in a direction of theferrite structure and the four windings.
 13. The WPT pad apparatus ofclaim 1, wherein each of the four windings comprises a spiral patternstarting at an edge of a winding center section and expanding away fromthe center section, the center section comprising an area withoutconductors at a center of a winding.
 14. The WPT pad apparatus of claim13, wherein each winding of the four windings comprises two or morewinding sections wound in parallel and each winding section is connectedto a capacitor located at the center section of the winding.
 15. The WPTpad apparatus of claim 13, wherein the center section of each windingcomprises a ferrite chimney coupled to the horizontal surface of theferrite structure and extending in a direction transverse to thehorizontal surface at least a a thickness of the winding associated withthe center section.
 16. The WPT pad apparatus of claim 1, wherein eachof the four windings comprises a conductor, each conductor comprisesmultiple strands, the strands electrically isolated from each other, theconductor comprising a wide side and a narrow side, wherein the wideside of the conductor is oriented transverse to the horizontal surface.17. The WPT pad apparatus of claim 16, wherein the conductor is a litzwire.
 18. A wireless power transfer (“WPT”) pad apparatus comprising: aferrite structure; and four windings adjacent to the ferrite structure,wherein a horizontal surface of the ferrite structure is adjacent toeach of the four windings, each of the four windings wound in ahorizontal pattern that is planar to the horizontal surface, wherein thefour windings are arranged in a two-by-two square pattern in anorth-south-north-south polarity arrangement, wherein for adjacentwindings of the four windings, the ferrite structure comprises amagnetic pathway, and wherein a ferrite pathway between adjacentwindings of the four windings comprises a thickness and a width toprovide a low impedance, unsaturated magnetic pathway for anelectromagnetic field generated by the adjacent windings, and whereinthe ferrite structure comprises an opening in a center section, whereinthe center section is located at a center of the two-by-two squarepattern and the center section is external to each of the four windings.19. The WPT pad apparatus of claim 18, further comprising one or moreof: a vertical shield external to the ferrite structure positioned toshunt an electromagnetic field radiating in a direction horizontal withthe horizontal surface of the ferrite structure; and a ferrite chimneycoupled to the horizontal surface of the ferrite structure in the centersection of each winding and extending in a direction transverse to thehorizontal surface at least a thickness of the winding associated withthe center section.
 20. A wireless power transfer (“WPT”) systemcomprising: a first stage comprising one or more of a resonant converterand an alternating current (“AC”) to direct current (“DC”) converter,the first stage configured to wirelessly transmit power to a secondstage on a vehicle; a WPT pad apparatus that receives power from thefirst stage and transmits power wirelessly to a secondary pad of thesecond stage, the WPT pad apparatus comprising: a ferrite structure; andfour windings adjacent to the ferrite structure, wherein a horizontalsurface of the ferrite structure is adjacent to each of the fourwindings, each of the four windings wound in a horizontal pattern thatis planar to the horizontal surface, wherein the four windings arearranged in a two-by-two square pattern in a north-south-north-southpolarity arrangement.